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Implement custom diagnostic for ConstParamTy
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‎compiler/rustc_error_codes/src/error_codes/E0741.md‎

Lines changed: 8 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -10,15 +10,19 @@ struct A;
1010
struct B<const X: A>; // error!
1111
```
1212

13-
Only structural-match types (that is, types that derive `PartialEq` and `Eq`)
14-
may be used as the types of const generic parameters.
13+
Only structural-match types, which are types that derive `PartialEq` and `Eq`
14+
and implement `ConstParamTy`, may be used as the types of const generic
15+
parameters.
1516

16-
To fix the previous code example, we derive `PartialEq` and `Eq`:
17+
To fix the previous code example, we derive `PartialEq`, `Eq`, and
18+
`ConstParamTy`:
1719

1820
```
1921
#![feature(adt_const_params)]
2022
21-
#[derive(PartialEq, Eq)] // We derive both traits here.
23+
use std::marker::ConstParamTy;
24+
25+
#[derive(PartialEq, Eq, ConstParamTy)] // We derive both traits here.
2226
struct A;
2327
2428
struct B<const X: A>; // ok!

‎compiler/rustc_hir_analysis/src/check/wfcheck.rs‎

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -836,7 +836,7 @@ fn check_param_wf(tcx: TyCtxt<'_>, param: &hir::GenericParam<'_>) {
836836
ObligationCause::new(
837837
hir_ty.span,
838838
param.def_id,
839-
ObligationCauseCode::WellFormed(Some(hir_ty.span)),
839+
ObligationCauseCode::ConstParam(ty),
840840
),
841841
wfcx.param_env,
842842
ty,

‎compiler/rustc_middle/src/traits/mod.rs‎

Lines changed: 3 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -445,6 +445,9 @@ pub enum ObligationCauseCode<'tcx> {
445445
/// Obligations to prove that a `std::ops::Drop` impl is not stronger than
446446
/// the ADT it's being implemented for.
447447
DropImpl,
448+
449+
/// Requirement for a `const N: Ty` to implement `Ty: ConstParamTy`
450+
ConstParam(Ty<'tcx>),
448451
}
449452

450453
/// The 'location' at which we try to perform HIR-based wf checking.

‎compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs‎

Lines changed: 110 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -149,6 +149,12 @@ pub trait TypeErrCtxtExt<'tcx> {
149149
root_obligation: &PredicateObligation<'tcx>,
150150
error: &SelectionError<'tcx>,
151151
);
152+
153+
fn report_const_param_not_wf(
154+
&self,
155+
ty: Ty<'tcx>,
156+
obligation: &PredicateObligation<'tcx>,
157+
) -> DiagnosticBuilder<'tcx, ErrorGuaranteed>;
152158
}
153159

154160
impl<'tcx> InferCtxtExt<'tcx> for InferCtxt<'tcx> {
@@ -641,6 +647,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
641647
span = obligation.cause.span;
642648
}
643649
}
650+
644651
if let ObligationCauseCode::CompareImplItemObligation {
645652
impl_item_def_id,
646653
trait_item_def_id,
@@ -657,6 +664,13 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
657664
return;
658665
}
659666

667+
// Report a const-param specific error
668+
if let ObligationCauseCode::ConstParam(ty) = *obligation.cause.code().peel_derives()
669+
{
670+
self.report_const_param_not_wf(ty, &obligation).emit();
671+
return;
672+
}
673+
660674
let bound_predicate = obligation.predicate.kind();
661675
match bound_predicate.skip_binder() {
662676
ty::PredicateKind::Clause(ty::Clause::Trait(trait_predicate)) => {
@@ -1163,6 +1177,102 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
11631177
self.point_at_returns_when_relevant(&mut err, &obligation);
11641178
err.emit();
11651179
}
1180+
1181+
fn report_const_param_not_wf(
1182+
&self,
1183+
ty: Ty<'tcx>,
1184+
obligation: &PredicateObligation<'tcx>,
1185+
) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
1186+
let span = obligation.cause.span;
1187+
1188+
let mut diag = match ty.kind() {
1189+
_ if ty.has_param() => {
1190+
span_bug!(span, "const param tys cannot mention other generic parameters");
1191+
}
1192+
ty::Float(_) => {
1193+
struct_span_err!(
1194+
self.tcx.sess,
1195+
span,
1196+
E0741,
1197+
"`{ty}` is forbidden as the type of a const generic parameter",
1198+
)
1199+
}
1200+
ty::FnPtr(_) => {
1201+
struct_span_err!(
1202+
self.tcx.sess,
1203+
span,
1204+
E0741,
1205+
"using function pointers as const generic parameters is forbidden",
1206+
)
1207+
}
1208+
ty::RawPtr(_) => {
1209+
struct_span_err!(
1210+
self.tcx.sess,
1211+
span,
1212+
E0741,
1213+
"using raw pointers as const generic parameters is forbidden",
1214+
)
1215+
}
1216+
ty::Adt(def, _) => {
1217+
// We should probably see if we're *allowed* to derive `ConstParamTy` on the type...
1218+
let mut diag = struct_span_err!(
1219+
self.tcx.sess,
1220+
span,
1221+
E0741,
1222+
"`{ty}` must implement `ConstParamTy` to be used as the type of a const generic parameter",
1223+
);
1224+
// Only suggest derive if this isn't a derived obligation,
1225+
// and the struct is local.
1226+
if let Some(span) = self.tcx.hir().span_if_local(def.did())
1227+
&& obligation.cause.code().parent().is_none()
1228+
{
1229+
if ty.is_structural_eq_shallow(self.tcx) {
1230+
diag.span_suggestion(
1231+
span,
1232+
"add `#[derive(ConstParamTy)]` to the struct",
1233+
"#[derive(ConstParamTy)]\n",
1234+
Applicability::MachineApplicable,
1235+
);
1236+
} else {
1237+
// FIXME(adt_const_params): We should check there's not already an
1238+
// overlapping `Eq`/`PartialEq` impl.
1239+
diag.span_suggestion(
1240+
span,
1241+
"add `#[derive(ConstParamTy, PartialEq, Eq)]` to the struct",
1242+
"#[derive(ConstParamTy, PartialEq, Eq)]\n",
1243+
Applicability::MachineApplicable,
1244+
);
1245+
}
1246+
}
1247+
diag
1248+
}
1249+
_ => {
1250+
struct_span_err!(
1251+
self.tcx.sess,
1252+
span,
1253+
E0741,
1254+
"`{ty}` can't be used as a const parameter type",
1255+
)
1256+
}
1257+
};
1258+
1259+
let mut code = obligation.cause.code();
1260+
let mut pred = obligation.predicate.to_opt_poly_trait_pred();
1261+
while let Some((next_code, next_pred)) = code.parent() {
1262+
if let Some(pred) = pred {
1263+
let pred = self.instantiate_binder_with_placeholders(pred);
1264+
diag.note(format!(
1265+
"`{}` must implement `{}`, but it does not",
1266+
pred.self_ty(),
1267+
pred.print_modifiers_and_trait_path()
1268+
));
1269+
}
1270+
code = next_code;
1271+
pred = next_pred;
1272+
}
1273+
1274+
diag
1275+
}
11661276
}
11671277

11681278
trait InferCtxtPrivExt<'tcx> {

‎compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs‎

Lines changed: 2 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -2655,7 +2655,8 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
26552655
| ObligationCauseCode::BinOp { .. }
26562656
| ObligationCauseCode::AscribeUserTypeProvePredicate(..)
26572657
| ObligationCauseCode::RustCall
2658-
| ObligationCauseCode::DropImpl => {}
2658+
| ObligationCauseCode::DropImpl
2659+
| ObligationCauseCode::ConstParam(_) => {}
26592660
ObligationCauseCode::SliceOrArrayElem => {
26602661
err.note("slice and array elements must have `Sized` type");
26612662
}

‎src/tools/clippy/tests/ui/same_functions_in_if_condition.rs‎

Lines changed: 3 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -10,6 +10,8 @@
1010
clippy::uninlined_format_args
1111
)]
1212

13+
use std::marker::ConstParamTy;
14+
1315
fn function() -> bool {
1416
true
1517
}
@@ -96,7 +98,7 @@ fn main() {
9698
};
9799
println!("{}", os);
98100

99-
#[derive(PartialEq, Eq)]
101+
#[derive(PartialEq, Eq, ConstParamTy)]
100102
enum E {
101103
A,
102104
B,

‎src/tools/clippy/tests/ui/same_functions_in_if_condition.stderr‎

Lines changed: 12 additions & 12 deletions
Original file line numberDiff line numberDiff line change
@@ -1,11 +1,11 @@
11
error: this `if` has the same function call as a previous `if`
2-
--> $DIR/same_functions_in_if_condition.rs:37:15
2+
--> $DIR/same_functions_in_if_condition.rs:39:15
33
|
44
LL | } else if function() {
55
| ^^^^^^^^^^
66
|
77
note: same as this
8-
--> $DIR/same_functions_in_if_condition.rs:36:8
8+
--> $DIR/same_functions_in_if_condition.rs:38:8
99
|
1010
LL | if function() {
1111
| ^^^^^^^^^^
@@ -16,61 +16,61 @@ LL | #![deny(clippy::same_functions_in_if_condition)]
1616
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
1717

1818
error: this `if` has the same function call as a previous `if`
19-
--> $DIR/same_functions_in_if_condition.rs:42:15
19+
--> $DIR/same_functions_in_if_condition.rs:44:15
2020
|
2121
LL | } else if fn_arg(a) {
2222
| ^^^^^^^^^
2323
|
2424
note: same as this
25-
--> $DIR/same_functions_in_if_condition.rs:41:8
25+
--> $DIR/same_functions_in_if_condition.rs:43:8
2626
|
2727
LL | if fn_arg(a) {
2828
| ^^^^^^^^^
2929

3030
error: this `if` has the same function call as a previous `if`
31-
--> $DIR/same_functions_in_if_condition.rs:47:15
31+
--> $DIR/same_functions_in_if_condition.rs:49:15
3232
|
3333
LL | } else if obj.method() {
3434
| ^^^^^^^^^^^^
3535
|
3636
note: same as this
37-
--> $DIR/same_functions_in_if_condition.rs:46:8
37+
--> $DIR/same_functions_in_if_condition.rs:48:8
3838
|
3939
LL | if obj.method() {
4040
| ^^^^^^^^^^^^
4141

4242
error: this `if` has the same function call as a previous `if`
43-
--> $DIR/same_functions_in_if_condition.rs:52:15
43+
--> $DIR/same_functions_in_if_condition.rs:54:15
4444
|
4545
LL | } else if obj.method_arg(a) {
4646
| ^^^^^^^^^^^^^^^^^
4747
|
4848
note: same as this
49-
--> $DIR/same_functions_in_if_condition.rs:51:8
49+
--> $DIR/same_functions_in_if_condition.rs:53:8
5050
|
5151
LL | if obj.method_arg(a) {
5252
| ^^^^^^^^^^^^^^^^^
5353

5454
error: this `if` has the same function call as a previous `if`
55-
--> $DIR/same_functions_in_if_condition.rs:59:15
55+
--> $DIR/same_functions_in_if_condition.rs:61:15
5656
|
5757
LL | } else if v.pop().is_none() {
5858
| ^^^^^^^^^^^^^^^^^
5959
|
6060
note: same as this
61-
--> $DIR/same_functions_in_if_condition.rs:57:8
61+
--> $DIR/same_functions_in_if_condition.rs:59:8
6262
|
6363
LL | if v.pop().is_none() {
6464
| ^^^^^^^^^^^^^^^^^
6565

6666
error: this `if` has the same function call as a previous `if`
67-
--> $DIR/same_functions_in_if_condition.rs:64:15
67+
--> $DIR/same_functions_in_if_condition.rs:66:15
6868
|
6969
LL | } else if v.len() == 42 {
7070
| ^^^^^^^^^^^^^
7171
|
7272
note: same as this
73-
--> $DIR/same_functions_in_if_condition.rs:62:8
73+
--> $DIR/same_functions_in_if_condition.rs:64:8
7474
|
7575
LL | if v.len() == 42 {
7676
| ^^^^^^^^^^^^^

‎tests/incremental/const-generics/hash-tyvid-regression-1.rs‎

Lines changed: 13 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -1,8 +1,20 @@
11
// revisions: cfail
22
#![feature(generic_const_exprs, adt_const_params)]
33
#![allow(incomplete_features)]
4+
5+
use std::marker::ConstParamTy;
6+
7+
#[derive(PartialEq, Eq, ConstParamTy)]
8+
struct NonZeroUsize(usize);
9+
10+
impl NonZeroUsize {
11+
const fn get(self) -> usize {
12+
self.0
13+
}
14+
}
15+
416
// regression test for #77650
5-
fn c<T, const N: std::num::NonZeroUsize>()
17+
fn c<T, const N: NonZeroUsize>()
618
where
719
[T; N.get()]: Sized,
820
{

‎tests/incremental/const-generics/hash-tyvid-regression-2.rs‎

Lines changed: 14 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -1,11 +1,23 @@
11
// revisions: cfail
22
#![feature(generic_const_exprs, adt_const_params)]
33
#![allow(incomplete_features)]
4+
5+
use std::marker::ConstParamTy;
6+
7+
#[derive(PartialEq, Eq, ConstParamTy)]
8+
struct NonZeroUsize(usize);
9+
10+
impl NonZeroUsize {
11+
const fn get(self) -> usize {
12+
self.0
13+
}
14+
}
15+
416
// regression test for #77650
5-
struct C<T, const N: core::num::NonZeroUsize>([T; N.get()])
17+
struct C<T, const N: NonZeroUsize>([T; N.get()])
618
where
719
[T; N.get()]: Sized;
8-
impl<'a, const N: core::num::NonZeroUsize, A, B: PartialEq<A>> PartialEq<&'a [A]> for C<B, N>
20+
impl<'a, const N: NonZeroUsize, A, B: PartialEq<A>> PartialEq<&'a [A]> for C<B, N>
921
where
1022
[B; N.get()]: Sized,
1123
{

‎tests/incremental/const-generics/try_unify_abstract_const_regression_tests/issue-77708-3.rs‎

Lines changed: 12 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -2,7 +2,18 @@
22
#![feature(generic_const_exprs, adt_const_params)]
33
#![allow(incomplete_features)]
44

5-
use std::{convert::TryFrom, num::NonZeroUsize};
5+
use std::{convert::TryFrom};
6+
7+
use std::marker::ConstParamTy;
8+
9+
#[derive(PartialEq, Eq, ConstParamTy)]
10+
struct NonZeroUsize(usize);
11+
12+
impl NonZeroUsize {
13+
const fn get(self) -> usize {
14+
self.0
15+
}
16+
}
617

718
struct A<const N: NonZeroUsize>([u8; N.get()])
819
where

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